This invention relates to the polar solvent treatment of n-dodecyl mercaptoethanol (DMD-1) made with a triethylamine (TEA) catalyst.
The reaction between ethylene oxide and n-dodecyl mercaptan giving n-dodecyl mercaptoethanol using a basic catalyst is a well known. N-dodecyl mercaptoethanol is desirable because of its value as a specialty chemical and its use in the preparation of many products. Basic catalysts are generally preferred in the production of n-dodecyl mercaptoethanol because basic catalysts allow for the desired consumption of the mercaptan reactant before forming polyethylene glycols and dioxanes.
Purification of the n-dodecyl mercaptoethanol and the general removal of residual basic catalyst after completion of the reaction is one of the problems encountered in n-dodecyl mercaptoethanol production. Purification through distillation at high temperatures is typically not performed because n-dodecyl mercaptoethanol decomposes at high temperatures, and therefore would require a high vacuum system for distillation. Because such high vacuum systems are not generally available on a commercial, large-scale operation, an alternative purification scheme allowing the stripping of the residual catalyst is necessary.
Sodium hydroxide is commonly used as the basic catalyst in the reaction of ethylene oxide with n-dodecyl mercaptan to form the n-dodecyl mercaptoethanol. The sodium hydroxide has good catalytic activity, but the purification of the product away from the residual catalyst has been found to be difficult. Leaving the residual sodium hydroxide catalyst with the product is not practical because the sodium hydroxide forms a noticeable residue in the product. One method of stripping the residual catalyst from the product involves converting the sodium hydroxide into sodium bicarbonate which is in turn removed by filtration. This method, however, is time-consuming. Another method involves using water to wash the sodium hydroxide from the product, but this is unsatisfactory because undesirable water is left in the product. Thus, although production of n-dodecyl mercaptoethanol is possible with the sodium hydroxide catalyst, alternative catalytic methods are desirable.
Use of the basic catalyst system employing triethylamine as the catalyst represents one alternative to the sodium hydroxide system for production of n-dodecyl mercaptoethanol, as shown in the art in Chemical Abstracts 83: 95961; 99: 157545; and 107: 77079. The purification problem, however, is even more emphasized with the use of the triethylamine catalyst. The residual catalyst and other amine impurities formed during the reaction leave the n-dodecyl mercaptoethanol product with a very unpleasant and offensive odor in addition to leaving the n-dodecyl mercaptoethanol discolored. Pure n-dodecyl mercaptoethanol is found as a white, waxy solid with the low melting point of 33.degree. C. The impurities found in the n-dodecyl mercaptoethanol produced using the triethylamine catalyst leave the compound with an undesirable yellow-brownish color. Thus, although TEA represents a very useful catalyst in terms of producing n-dodecyl mercaptoethanol, the n-dodecyl mercaptoethanol is left commercially undesirable because of residual amine impurities.
Various unsuccessful efforts have been made in the attempt to remov the offensive odor and undesired coloration left when TEA is used as a catalyst. For example, when the crude n-dodecyl mercaptoethanol is contacted with the polar solvent methanol (Boiling Point 69.degree. C.), followed by heat under vacuum, neither the color nor odor improved. Similarly, the non-polar solvent heptane (Boiling Point 98.4.degree. C.) also failed to correct the odor and color problems of the crude n-dodecyl mercaptoethanol. Further, the use of nitrogen as a gaseous stripping agent is also ineffective against the odor and coloration problems.